This invention concerns a method of determining the angle of roll of a launchable body which rotates in its path, such as a rotating projectile, shell, guided missile or the like which is launched from a launching device, in which a transmitter with antenna arranged in connection with the launching device communicates with a receiver with antenna arranged in the launchable body. The invention also concerns an arrangement for determining the angle of roll of a launchable body which rotates in its path, such as a rotating projectile, shell, guided missile or the like, which is launched from a launching device, comprising a transmitter with antenna arranged in connection with the launching device and a receiver with antenna arranged in the launchable body.
Methods and arrangements for determining the angle of roll of rotating bodies in similar circumstances are already known. For example, we can refer to U.S. Pat. No. 4,750,689 and EP A1 341 772. Both these documents show embodiments for determining the angle of roll by the utilization of polarized waves which are detected by means of two so-called frame antennas arranged in the rotating body and turned through 90 degrees in relation to each other. This involves a relatively bulky antenna arrangement and among other things the possibility of locating parts of the antenna in the fins of the rotating body is discussed. Another known embodiment is described in our U.S. Pat. No. 5,414,430 and in this case a phase-modulated polarized carrier wave is transmitted from which the angle of roll can be determined in the receiver of the rotating body. According to another embodiment known through our U.S. Pat. No. 5,163,637 a transmitted long-wave signal and a transmitted microwave signal are used for the determination in the rotating body of its angle of roll. The embodiments according to these two last-mentioned patents also require relatively bulky antenna arrangements in the rotating body.
The present invention proposes another solution which like the embodiment according to our U.S. Pat. No. 5,414,430 utilizes only one signal, preferably within the microwave range, to determine the angle of roll. According to the invention sweeping beams are used. Both the transmitter antenna and the receiver antenna are designed with a sweeping beam. The beams coincide for a longer or shorter period of time depending upon whether the beams are sweeping with each other or towards each other. For each half revolution which the rotating body rotates, the beams change between sweeping towards each other and sweeping with each other. The rotation position is determined unambiguously by measuring the time when the beams coincide and the signal strength which is obtained during the periods of time when the beams coincide. The problem of determining unambiguously whether it is the first half or second half of a rotation revolution has a simple solution in that the beams have periods of coincidence of different lengths in the two halves of the rotation revolution. In order to determine the angle within a half revolution the signal strengths are studied which arise in the receiver antenna when the beams coincide.
The invention solves the problem of ambiguity while at the same time an easily locatable and compact antenna arrangement can be arranged in the rotating body. The principal characteristics of the method according to the invention are that the transmitter antenna and receiver antenna are each designed with their sweeping beams directed principally towards each other, that the beam of the transmitter antenna sweeps in a fixed plane relative to the launching device, that the beam of the receiver antenna sweeps in a fixed plane relative to the launchable body, that the time the two beams coincide is detected and that the signal strength during the time the beams coincide is recorded to create an imaginary rotation envelope and that the angle of roll is determined based on the measured times and created imaginary rotation envelope. The principal characteristics of the arrangement for determining the angle of roll are that the transmitter antenna and receiver antenna are designed with sweeping beams and that the receiver comprises devices for processing received signal information concerning time and signal strength during the time the sweeping beams coincide.
According to a suitable method the transmitter and receiver antennas are dimensioned to work within the millimeter wave range, preferably within the frequency range 35-45 GHz. The receiver antenna is advantageously constructed of electrically controllable antenna elements in the form of dipole slots. Such a receiver antenna is very suitable for the frequency range proposed above and is easy to house in the rear part of the rotating body.
In order to ensure good interaction between the sweeping beams it is proposed according to an advantageous method that the sweeping beam of the receiver antenna is kept zeroed during the moment of launching and that the time interval between the interceptions of the beam of the transmitter antenna with the zeroed beam of the receiver antenna is measured and that after the abovementioned measuring and based on the measurement result the sweep of the receiver antenna is started in order to intercept the transmitter""s sweep at approximately 0 degrees.
Additional characteristics of the invention are apparent from the attached patent claims.